Compared with other motors, a brushless DC motor exhibits advantages of energy saving and high reliability and has become increasingly popularized. Single-phase DC driving is achieved by a single H-bridge inverter with a Hall-effect sensor. In addition, a conventional three-phase DC motor, with or without a sensor, is typically driven by three half-bridges, and has phase coil windings that are typically configured in a star shape. As shown in FIG. 1, three phase coil windings 1 have a common terminal. Trapezoidal or sinusoidal magnetic field orientation control is the most common commutation method. However, in such a case, a voltage or current output by the inverter has a shape only similar to sine, and a brushless DC motor driven by such a voltage or current may cause large power consumption and audible noises.